1. Field of the Invention
The present invention relates to a solder alloy for soldering which is used as a material for mounting electronic parts, and more particularly, to a solder alloy exhibiting an improved fatigue-proof characteristic in a soldering area.
2. Description of the Related Art
Soldering is used mainly for mounting small electronic parts such as a semiconductor ship or a resistor chip on a printed circuit board (PCB). Since the PCB, the electronic parts and the solder alloy usually have different thermal expansion coefficients, the soldering area in a PCB on which parts are mounted at high density is subject to thermal stress generated by heat during soldering so that the grain of the soldering area becomes coarse. Since the soldering area having a coarse grain is brittle, the area can easily crack due to repetitive stresses of external impacts or vibrations. For instance, a fatal defect such as disconnection of a wire of the parts mounted on the board can occur. Therefore, a surface mounting technology using advanced soldering is required to keep pace with the current trends of mounting parts very densely for a compact and light electronic product maintaining superior functionality.
Furthermore, although a binary-eutectic solder alloy of tin (Sn) and lead (Pb) has been used as main constituents, the above-described problem becomes serious since a print pattern and a soldering land of a PCB becomes narrower as in the case of mounting parts at high-density which reduces the amount of lead consumed during soldering.